code: def test_stack_predictions(self):
      result = object_detection_format.stack_predictions(
          _STACK_SPLITFORMAT,
          ["xmin", "ymin", "xmax", "ymax", "class_id"],
      )
      result = object_detection_format.truncate_by_num_detections(
          _STACK_SPLITFORMAT, "num_detections", result
      )
      np.testing.assert_allclose(result, _STACK_RESULT[:1])
  
file_path: model-analysis/tensorflow_model_analysis/metrics/preprocessors/utils/object_detection_format_test.py
imports: from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  from tensorflow_model_analysis import constants
  from tensorflow_model_analysis.metrics.preprocessors.utils import object_detection_format
  from tensorflow_model_analysis.utils import util
label_desc: Use image node_id 2 for calling the ObjectDetectionFormatTest obj's underlying member method code with example usage: obj.test_stack_predictions() without return types